The Seine was seen as an open-air garbage dump. It was former French president Jacques Chirac who first proposed the idea of swimming in the Seine in 1990. Now, almost three decades later, it is the current mayor, Anne Hidalgo, who has taken up the idea. She has made it one of the pillars of her bid to host the 2024 Olympics. Some 1.4 billion has been spent on pollution control and she promised: "Next month you will be able to swim in the Seine."

Everything is on schedule and even city beaches are being considered. It's been a century since swimming was banned and the dreams of Parisians were shattered. Now, thanks to the Paris Olympics, floating on your back under the Eiffel Tower could be possible.

The river will host the triathlon and swimming marathon, and will be the star of the opening ceremony on 26 July. As in Zurich and Munich, one of three new urban "beaches" will open in Paris under the windows of the City Hall, with another at the foot of the Eiffel Tower. Nearly 30 more are planned. They will be located in the suburbs and along the Marne River, which flows into the Seine to the east of the French capital.

It is hard to believe that, after so many doubts, this will happen, as it did in the 18th century with scenes of Parisians bathing naked in the Seine. After storms, the Seine tends to fluctuate wildly. Sometimes it takes one step forward and two steps back. Swimming and Triathlon officials were looking for a plan B if the water tests weren't met. Unusually heavy rainfall and a faulty valve in the sewage system were blamed..

Reigning Olympic marathon champion Ana Marcela Cunha called for this 'Plan B', as quoted by AFP: "The health of the athletes should come first." Lifeguard Gaelle Deletang, a member of the French capital's aquatic civil defence team, had "diarrhoea and a rash" after swimming in the Seine.

The river looked brown. Several other volunteers "had a virus for three weeks... and everyone had stomach problems," she added. Young adventurer Arthur Germain, who happens to be the son of the mayor of Paris, also came across "areas where I had trouble breathing" due to industrial and agricultural pollution when he swam the entire 777 kilometres of the Seine in 2021.

The river is full of surprises. In the summer of 2022, the Seine passed EU water quality tests at three points in Paris, after failing at all 14 points in the capital last year. Despite all the scepticism, he tells AFP, "We will do it. Remi Delorme, captain of a boat that has been collecting rubbish from the river since 1980. Sofas, scooters, dead animals and once or twice a year human corpses. You get used to it." However, the amount of rubbish is decreasing year by year, from a maximum of 325 tonnes to 190 tonnes in 2020.

The push to make the Seine swimmable for the Olympics is the key. The French government has stepped up its efforts. "Uncontrolled flushing has a major impact on faecal bacteria in the river," says Jean-Marie Mouchel, professor of hydrology at the Sorbonne University. Another problem was the leaky sewage pipes of some 23,000 homes in the suburbs. Shower and toilet water was being dumped directly into the environment.

The return of the fish is another reason for optimism. While the Seine "has not become a wild river", it now has "more than 30 species of fish, compared to three in 1970", says the professor. Bill François, who fishes up to five times a week near the Pont Marie in the historic heart of Paris, caught a surprisingly large catfish on the day he spoke to AFP. It was a species he had never expected to find in the Seine.

For microbiologist Françoise Lucas, who has been following efforts to clean up the Seine for years, the weather will ultimately decide the fate of the Olympic events on the river. "Everything that can be done (technically) has already been done," Lucas told AFP.

Not far away, a new rainwater control station is in operation. 50 metres wide and 30 metres deep, it can hold the equivalent of 20 Olympic swimming pools. It is a veritable underground cathedral designed to prevent rainwater from overflowing into the sewers and the Seine.

"We had forgotten about the Seine," said Stéphane Raffalli, mayor of the riverside Paris suburb of Ris-Orangis. "There are people who have lived here for years and have never taken a walk on the banks." Yet suburbanites swam in the Seine until the 1960s and in the Marne until the 1970s. 

"We have carried out pollution studies over a long period of time. It is safe to swim in the river," the mayor insisted. With climate change and the prospect of summer temperatures in Paris reaching 50 degrees Celsius, the need for a place to cool off in the summer has never been greater.

However, some have taken the plunge. On Île Saint Denis, where the Olympic Village is being built. Josué Remoue swims in the river three times a month, from May to October "I've never been ill," says the 52-year-old civil servant. He goes on Sundays or in the evening to avoid the boat traffic. 

On the night that the AFP joined his group, the water was a little earthy, but it was not murky at all. With a temperature of 25 degrees Celsius, the scene along the riverbank was almost bucolic, despite the buildings nearby. "It's very different from swimming in a pool," said Céline Debunne, 47, as she emerged from what she called "a super two-kilometre swim ... I love swimming like this." The Olympics could change Paris forever.